Conventionally, when operation data of a car for each operation is recorded in a memory such as a nonvolatile recording medium within an IC memory card, for example, the recording has been made according to the format as shown in FIG. 6. Referring to FIG. 6, reference numeral 1 denotes a memory in which one word is formed of eight bits (one byte). In the memory 1, there are formed a data region M1 and an ID region M2. The data region M1 is further divided into a distance data recording region M11 partitioned into sections, each section corresponding to each operation, used for successively recording therein the travel distance data compressed by a predetermined compression method, and a speed data recording region M12 also partitioned into sections, each section corresponding to each operation, used for successively recording therein the speed data compressed by the predetermined compression method. The IC memory card is removably mounted into an operation recorder installed on a car. One operation is defined, for example, as the time interval between the mounting of an IC memory card into the operation recorder and the removal of the same from the recorder, whereas the starting time and the ending time of each operation are also recorded on the basis of time data generated by a clock incorporated in the operation recorder.
In the ID region M2, there are recorded such data as the allowance, resolution, and sampling time for each operation, addresses in the regions M11 and M12 at which the final data of the travel distance data and the speed data for each operation are recorded, records as to whether or not the time correction of the clock was made and the number of times of the correction was made, and time correction data. The time correction data is constituted of data related to the time before correction and the time after correction. The time of the clock when a correcting button is operated, which button is provided on the operation recorder to be operated at the start of a time correction, is recorded as the time-before-correction data, whereas the time of the clock when a set button to be operated at the end of a time correction is operated after the time correction is finished by having the clock set forward or backward is recorded as the time-after-correction data.
The IC memory card as the recording medium having the operation data recorded therein as described above is removed from the operation recorder and mounted into an analyzer for analyzing digital operation record. Analyses of each operation are thereby made. As one of the results provided by such analytical processing, the momentarily varying car speed during each operation is arranged in the form of graph to be displayed on the screen of the CRT or printed in a sheet of paper so that the operational state is seen at a glance.
In such a case, based on the collected speed data, and the starting time and ending time, speed varying with time is graphed, having the time taken along the abscissa and the speed taken along the ordinate. When time correction is made in the middle of an operation as described above, the display of the speed is made after executing an additional process using the time correction data then obtained thereby correcting the time axis.
The manner in which the above described correction data is recorded will be described below. When the time of the clock is 20 minutes fast, i.e., 20 minutes faster than the true time, if the correction button indicating the start of a time correction is operated at 1:10, for example, and then the clock is set to 0:50 and the set button indicating the end of the time correction is operated without any time loss in the meantime, "1:10" is recorded as the time data before correction and "0.50" is recorded as the time data after correction. Thus, the starting time of the operation can be corrected to 0:00 according to the time data before correction "1:10" and the time data after correction "0:50".
In reality, it is seldom that the time correction is carried out as described above, but it is carried out in the following manner.
Supposing that the operation of the car was started at the point of time t1, for example, as shown in FIG. 8, "0:20" is recorded as the starting time of operation according to the time data then provided by the clock incorporated in the recorder. If, thereafter, it is noticed that the clock is fast and the correction button indicating the start of a time correction is operated at the point of time t2, then, "1:10" is recorded as the time data before correction according to the time data provided by the clock at that time. Then, ten minutes after the time data is recorded if the clock is set backward a suitable time and the set button indicating the end of the time correction is operated while setting the clock with the radio time signal at 1:00, "1:00" is recorded as the time data after correction according to the time data provided by the clock at that time.
When, as described above, "1:10" was recorded as the time data before correction and "1:00" was recorded as the time data after correction, the analyzer side will take it wrong that the clock was set backward by 10 minutes. Then, if the analyzer side corrects the data of time of the start of operation using such time data for correction, it will conclude that the operation was made for 6 hours and 50 minutes from 0:10 to 7:00, not agreeing with the actual operation time of 7 hours. Once such disagreement is produced, it becomes troublesome to deal with the 10-minute data when displaying or printing the state of operation in the form of a graph, and in some case, such a problem occurs that the data in question becomes missing or overlapped.